Sensing device having adjustable threshold response



April 1953 H. B. SCHULTHEIS ETAL 2,636,386

SENSING DEVICE HAVING ADJUSTABLE THRESHOLD RESPONSE Filed May 23, 1949 JNVENTORS AND HARRY B. SCHULTHE/S LOUIS A. G. TER -VEEN Patented Apr. 28, 1953 SENSING DEVICE HAVING ADJUSTABLE THRESHOLD RESPONSE Harry B. Schultheis, Pacoima, and Louis A. G. ter Veen, North Hollywood, Calif., assignors to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application May 23, 1949, Serial No. 94,918

3 Claims.

This invention relates to sensing devices for producing electrical values proportional to the magnitude of a condition to be measured.

An object of the invention is to provide a sensing device, the threshold response of which can be adjusted to meet the requirements of the particular situation.v

A more specific object is to provide a pressure sensing device the threshold response of which can be accurately adjusted to respond to a desired minimum pressure.

Other more specific objects and features of the invention will appear from the description to fol low.

Briefly stated, as applied to pressure sensing, the invention comprises a modification of prior known pressure sensing devices of the typein which a Bourdon tube constitutes the mechanical element movable in response to pressure changes. In a conventional sensing device of this type, the Bourdon tube assumes its normal, unstressed position'at zero pressure; hence in conventional devices, if the tube is not to have excessive movement when measuring high pressures it must be made-relatively stifi, which naturally reduces the sensitivity of response to small pressure changes.

Where the entire range of pressures from zero to a high'value must be'sen'sed, there is no escape from the use of a stiii tube, and the resultant-lack of sensitivity; However, in accordance with this invention, where only a limited range of high pressures is to be sensed, good-sensitivity within that range is obtained byemploying a relatively light tube, and placing in the path ofthe free end of the tubea limiting stop thatprevents it from returning ast the position corresponding to the lower endlof the range of pressures to be sensed. For successful use, the stop must be capable of very accurate adjustment and a feature of the present invention is a stop construction permitting. such accurate adjustment and a jig for facilitating the adjustment.

A particular embodiment of the invention will now be described in detail with reference to the 4 drawing, in which:

Fig. 1 is a top or plan view of a pressure sensing instrument incorporating the invention;

Fig. 2 is an end viewlooking at the left end of Fig. 1;

Fig. 3 is a longitudinal section taken in the plane III-III of Figs, 1 and 2 -Fig. 4 is a cross section taken: in the plane IV--IV of Fig. 3; and

Fig. 5 is a plan view showing a portion of the ing section In by screws 12, and closed at its left end by a cup 1 3 which contains a variable inductance element [4.

The pressure-responsive portion of the instrument is mounted on the end section II and comprises a resilient member in the form of a Bourdon tube 15 which is anchored at its right end, as by brazing [6, to the end section II and is connected by a passage ll in the end section to a threaded nipple [8 whereby it can be connected through a conventional fitting to a tube [9 extending to the source of the pressure to be measured. The left or free end of the Bourdon tube 15 is closed, and has secured thereto, by a connecting element 2!], an armature 2| which is associated with the variable inductance element H. The latter, as shown, may be an inductor of the type commonly referred to as an E coil having a central leg 22 and end legs 23 with a winding 24 on the center leg. Commonly, three taps 25, 26 and 21 (Fig. 2) are taken off the winding 24, one from each end and. one from the middle of the winding, which are connected to an oscillating circuit, the E coil constituting one element of the tuner for the oscillator so that variations in the inductance of the winding 24 change the frequency of the oscillations, the frequency being a measure of the pressure being sensed. The inductanceof the winding 24 is of course varied in response to the movement of the armature 2| toward and away from the ends of the core elements 22 and 23.

Devices as manufactured in the past have corresponded generally to the structure so far described, the free end of the Bourdon tube -|5 being unrestrained mechanically, so that it was in a condition of rest under zero pressure. In accordance with the present invention, the device is adapted for responding to a range of pressures having as its lower limit a value well above zero, by providing a stop that limits return movement of the free end of the Bourdon tube.

This stop comprises a wedge 26 that issupported for longitudinal movement in a guideway 21 in a stationary member consisting of a block '28 mounted on or formed integrally with the casing end section II, one side of the guideway being constituted by a plate 29 secured to the block 28 by screws 30. By tightening the screws, the

wedge 26 can be locked in any position of longitudinal adjustment in the guideway 27. As best shown in Fig. 5, the outer face 32 of the wedge 26 is inclined longitudinally and bears against a 4 projection 35 on the right side of the connecting element 23, thereby limiting return movement of the free end of the Bourdon tube when the pressure therewithin is reduced. 7

In this way a relatively light Bourdon tube 15 can be employed to measure a range of relatively. high pressures, say from 500 to 1000 p. s, i., with;

relatively high sensitivity, because the entire 3 range oi.-:.movement1of the armature?- 2 I; toward and away? from the electromagnet' It is utilized within the desired range. On the other hand, if the stop were not employed, the Bourdon tube l5 would have to be made sufficiently stiff so that the total movement over the range from zero to 1000 p. s. i. would be within the permissible limits. Hence the movement of thearmature' 2l-within the desired range from 500 to 1000p; s. i. would only be half as great, and the sensitivity would be correspondingly reduced.

The wedge 26 is moved longitudinally to adjust the minimum pressure at which the projection 35 leaves the wedge. This adjustment was found rather diincult with conventional adjustingime'chanismsbut can be readily performed on that-wedge. 26 by means of; thejig' shown in Fi 5. This jig comprises a tubular casingelement 101 corresponding to .the casing section In in Fig; 1 butsdifiering therefrom in having a window-I02 and in havinga pair of adjusting screws I03. and i0 3 threaded through the. walls at'diametrically opposite points.

To efiectv adjustment, the end section 28- having the wedge 26 and Bourdon tube. l5, allas. shown inFig: 3, is prior to attachment to its own tubular casingsection :9 0, secured to the test jig ml, with its wedge 26 in alignment with the adjusting screws H93 and EM. Thepressure corresponding to the lower; end of the. desired pressure range is connected toa suitable oscillator. circuit having a frequency indicating ,meter. connected thereto. When the projection 35 is first.- displacedby. contact with the, surface 32 of the-wedge 26, the-ire.- quency meter will indicate a-change in frequency,

It. is to-be1 noted. that the adjustment. of the wedge to establish, the minimum pressure the device is to respond to is not necessarily related to-theadjustment of the spacing between the armature 2!. and. the pole iacesof the electromagnet. Hi.- ;-Ilowever, after the adjustment;of the .wedge hasbeencompleted, the end section! I is removed.v from the jig l0! and assembled t,o ,;its associated tubular casing gsection l0 containing the-electromagnet M. .Proper. ad-- justment of thetairv gap between the armatu-re 2i and-the pole faces of thee-electromagnet is thenmade by screwing thecut i3 inzort out ofthe casing l0. During-this adjustmenaa clamping ringclll isvery lightly clamped against a gasket 4 I to frictional ly restrain rotation, of the;

viousl applicable to other-types of sensing .de-' vices inwhich a resilient member is deflected in response to a phenomenon to be measured.

Although for the purpose of explaining the invention, a particular embodiment thereof has: been shown and described, obvious modifications will occurdso aperson skilled'zinftherarttand we do -notdesire to be limitedto-the exact" details shown and described.

v1. Asensingdevice comprising: a casing; a "resilient member anchored at one point to said casing and having a free portion proportionately deflectable 'inone'direction from a normal position of rest in response to a variation to be sensed over a range of values from zero to a large value;

electrical "means having an element mounted on said free portionfor producing electrical variations proportional to deflection of said free portion; a-stationary member anchored to said casing and having a wedge guideway adjacent to said free portion of saidresilient.member and; extending substantially;-perpendicular;:to" ithe1pathe'of deflection. of said free portion; zawedge seatedzin saidguideway for longitudinalmovement'therein and having an inclined face for: contactingisaid portion over a range of"longitudinalpositions of the wedge in said guidewayrthewedge-variably stepping the return movementoi'asaid :free portion at'diiierent-peints in aitspath accordingzto the longitudinal position; 1 of I the wedgezsini said guideway; and means fonilocking: said wedgerin positionqof adjustment in the: guideway;

.A sensing device;according/toclaimi.1.:in which said casing comprises two separable sec tions on the first of-:- which said resilient: element andwedge are mounted, the second section coop.- erating' with saide-first section to form". amenclosure; said; second section havingoadjustingscrews engageable with? opposite -a ends of said wedge for accurately. shifting it, andhavingian opening for access to said wedgelocking means;

-13. A- sensing Idevice comprisingz-za casing;.=:a resilient member: anchored :to; said i casing-=.- and having. a tree portion proportionately deflectable in" one direction. froma' normal 'POSitiQIllOfl-IGS} inresponse to a'variation to be sensedr'overea range of values from zerotoialarge value; elec-- trical means having an element-mounted onrsaid free portion for producing 5: electrical: variations proportional. to deflection of saidxfree portionzxa stationary. member: anchored to'said casingand having 'awedgev backing-"surfaceextending substantially perpendicular to the 'path of deflection of said free portionya-wedge adjustably movable along" said surface" "andoriented to present different-- thicknesses between. said backing surface and said .free portionin difierentposi tions of movement,; and" screw: means forfa'ccu rately moving said wedge" along: said backing" surface;

" HARRY; J3. .TSCHULTHEIS; L'QIJIsf-A. 1 G'... rm

' References. LCitedi in the file. Of this .patent 

